1. Field of the Invention
The present invention relates to an electrophotographic image forming device used in printers, copy machines, and facsimile machines and more particularly to a cleanerless image forming device wherein a photosensitive drum is cleaned using a cleanerless method.
2. Description of the Related Art
Electrophotographic type image forming devices are provided with: a photosensitive drum; a charge device for forming a uniform charge on the surface of the photosensitive drum; an exposure unit for exposing the surface of the photosensitive drum with light to form an electrostatic latent image; a developing unit for developing the electrostatic latent image using toner charged with a predetermined positive or negative polarity, thereby forming a toner image on the surface of the photosensitive drum; and a transfer roller for transferring the toner image to a recording sheet.
After the toner image is transferred onto the recording sheet, some toner, depending on the density of the toner image, will remain untransferred on the surface of the photosensitive drum. During the next cycle of charging, exposure development, and transfer of a subsequent image on the photosensitive drum, this residual toner clinging to the surface of the photosensitive drum might be transferred to the next recording sheet where it is not required, thereby reducing the quality of the recorded image on the recording sheet.
Conventionally, a cleaner mechanism is provided to clean the residual toner off the photosensitive drum. One example of a cleaner mechanism is a blade for scraping residual toner from the surface of the photosensitive drum after completion of transfer processes. An alternative to a cleaner mechanism is a cleanerless method of forming images, wherein residual toner is recovered and reused by the development device.
In the cleanerless method, some type of leveling unit, such as a cleaning roller or a cleaning brush, is disposed in confrontation with the photosensitive drum at a position downstream from the transfer roller, that is, with respect to the rotational direction of the photosensitive drum. The leveling unit is capable of an adsorption mode, wherein it electrically adsorbs the residual toner from the photosensitive drum onto its surface, and also a release mode, wherein it releases the adsorbed toner from its surface back to the surface of the photosensitive drum.
The leveling unit enters its adsorption mode while image forming processes are being performed using the surface of the photosensitive drum. In order to periodically retrieve toner using the cleanerless system, the leveling unit enters its release mode while image forming processes are not being performed on the surface of the photosensitive drum, usually between supply. of sheets to the photosensitive drum. The toner returned to the surface of the photosensitive drum is transported to the developing unit of the image forming device by rotation of the photosensitive drum.
A cleanerless method which uses such a leveling unit is very effective. Even if positively or negatively charged toner remains on the surface of the photosensitive drum, the surface of the photosensitive drum can be sufficiently cleaned so that quality of images formed on the photosensitive drum can be maintained. Also, the residual toner is collected by the development roller and can be again used during subsequent development processes.
Because the leveling unit adsorbs residual toner from the surface of the photosensitive drum while images are being formed and releases the adsorbed toner back to the photosensitive drum while images are not being formed, the leveling means can maintain a high level of cleaning for long periods of time. As a result, the photosensitive drum can be maintained in a clean condition so that reductions in image quality caused by residual toner can be prevented.